[llvm] [WebAssembly] Disallow tail calls with byval arguments (PR #125142)
Thomas Lively via llvm-commits
llvm-commits at lists.llvm.org
Thu Jan 30 17:56:39 PST 2025
https://github.com/tlively updated https://github.com/llvm/llvm-project/pull/125142
>From 53f0accda525806ac222aacfcc7d524a7ae8fb9b Mon Sep 17 00:00:00 2001
From: Thomas Lively <tlively at google.com>
Date: Thu, 30 Jan 2025 16:19:28 -0800
Subject: [PATCH 1/2] [WebAssembly] Disallow tail calls with byval arguments
WebAssembly disallows tail calls with stack-allocated arguments because
they tail calls leave no way to fix up the stack pointer after the call.
WebAssembly also passes `byval` arguments on the stack, but we were not
considering them when deciding whether a tail call should be allowed.
Properly disallow tail calls in the presence of byval arguments and fix
the existing test that should have caught this.
Fixes #124443.
---
llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp | 7 +++++++
llvm/test/CodeGen/WebAssembly/tailcall.ll | 7 ++++---
2 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
index 02db1b142a22b54..4cc06f057a5760c 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -1211,6 +1211,13 @@ WebAssemblyTargetLowering::LowerCall(CallLoweringInfo &CLI,
}
}
}
+ // Similarly, we cannot tail call with byval arguments.
+ for (unsigned I = 0; I < CLI.Outs.size(); ++I) {
+ const ISD::OutputArg &Out = CLI.Outs[I];
+ if (Out.Flags.isByVal() && Out.Flags.getByValSize() != 0)
+ NoTail(
+ "WebAssembly does not support tail calling with stack arguments");
+ }
}
SmallVectorImpl<ISD::InputArg> &Ins = CLI.Ins;
diff --git a/llvm/test/CodeGen/WebAssembly/tailcall.ll b/llvm/test/CodeGen/WebAssembly/tailcall.ll
index 84bd142462e37e7..a1eeaf9f2e77e4c 100644
--- a/llvm/test/CodeGen/WebAssembly/tailcall.ll
+++ b/llvm/test/CodeGen/WebAssembly/tailcall.ll
@@ -296,12 +296,13 @@ define i32 @mismatched_byval(ptr %x) {
; CHECK-NEXT: global.set __stack_pointer, $pop7
; CHECK-NEXT: i32.load $push0=, 0($0)
; CHECK-NEXT: i32.store 12($1), $pop0
+; CHECK-NEXT: i32.const $push5=, 12
+; CHECK-NEXT: i32.add $push6=, $1, $pop5
+; CHECK-NEXT: call $0=, quux, $pop6
; CHECK-NEXT: i32.const $push3=, 16
; CHECK-NEXT: i32.add $push4=, $1, $pop3
; CHECK-NEXT: global.set __stack_pointer, $pop4
-; CHECK-NEXT: i32.const $push5=, 12
-; CHECK-NEXT: i32.add $push6=, $1, $pop5
-; CHECK-NEXT: return_call quux, $pop6
+; CHECK-NEXT: return $0
%v = tail call i32 @quux(ptr byval(i32) %x)
ret i32 %v
}
>From 8942dcbab0e867f59a8eeab7f774f9df870d1243 Mon Sep 17 00:00:00 2001
From: Thomas Lively <tlively at google.com>
Date: Thu, 30 Jan 2025 17:56:05 -0800
Subject: [PATCH 2/2] add tests for future improvements
---
llvm/test/CodeGen/WebAssembly/tailcall.ll | 103 ++++++++++++++++++++++
1 file changed, 103 insertions(+)
diff --git a/llvm/test/CodeGen/WebAssembly/tailcall.ll b/llvm/test/CodeGen/WebAssembly/tailcall.ll
index a1eeaf9f2e77e4c..c97b7a9d2c0dbe2 100644
--- a/llvm/test/CodeGen/WebAssembly/tailcall.ll
+++ b/llvm/test/CodeGen/WebAssembly/tailcall.ll
@@ -307,6 +307,109 @@ define i32 @mismatched_byval(ptr %x) {
ret i32 %v
}
+ at global = external global i32
+define i32 @mismatched_byval_location(ptr byval(i32) %x) {
+; CHECK-LABEL: mismatched_byval_location:
+; CHECK: .functype mismatched_byval_location (i32) -> (i32)
+; CHECK-NEXT: # %bb.0:
+; CHECK-NEXT: global.get $push2=, __stack_pointer
+; CHECK-NEXT: i32.const $push3=, 16
+; CHECK-NEXT: i32.sub $push9=, $pop2, $pop3
+; CHECK-NEXT: local.tee $push8=, $2=, $pop9
+; CHECK-NEXT: global.set __stack_pointer, $pop8
+; CHECK-NEXT: i32.const $push0=, 0
+; CHECK-NEXT: i32.load $push1=, global($pop0)
+; CHECK-NEXT: i32.store 12($2), $pop1
+; CHECK-NEXT: i32.const $push6=, 12
+; CHECK-NEXT: i32.add $push7=, $2, $pop6
+; CHECK-NEXT: call $1=, quux, $pop7
+; CHECK-NEXT: i32.const $push4=, 16
+; CHECK-NEXT: i32.add $push5=, $2, $pop4
+; CHECK-NEXT: global.set __stack_pointer, $pop5
+; CHECK-NEXT: return $1
+ %v = tail call i32 @quux(ptr byval(i32) @global)
+ ret i32 %v
+}
+
+declare i32 @quux2(ptr byval(i32), ptr byval(i32))
+
+define i32 @mismatched_byval_location_late(ptr byval(i32) %x, ptr byval(i32) %y) {
+; CHECK-LABEL: mismatched_byval_location_late:
+; CHECK: .functype mismatched_byval_location_late (i32, i32) -> (i32)
+; CHECK-NEXT: # %bb.0:
+; CHECK-NEXT: global.get $push3=, __stack_pointer
+; CHECK-NEXT: i32.const $push4=, 16
+; CHECK-NEXT: i32.sub $push12=, $pop3, $pop4
+; CHECK-NEXT: local.tee $push11=, $2=, $pop12
+; CHECK-NEXT: global.set __stack_pointer, $pop11
+; CHECK-NEXT: i32.load $push0=, 0($0)
+; CHECK-NEXT: i32.store 12($2), $pop0
+; CHECK-NEXT: i32.const $push1=, 0
+; CHECK-NEXT: i32.load $push2=, global($pop1)
+; CHECK-NEXT: i32.store 8($2), $pop2
+; CHECK-NEXT: i32.const $push7=, 12
+; CHECK-NEXT: i32.add $push8=, $2, $pop7
+; CHECK-NEXT: i32.const $push9=, 8
+; CHECK-NEXT: i32.add $push10=, $2, $pop9
+; CHECK-NEXT: call $0=, quux2, $pop8, $pop10
+; CHECK-NEXT: i32.const $push5=, 16
+; CHECK-NEXT: i32.add $push6=, $2, $pop5
+; CHECK-NEXT: global.set __stack_pointer, $pop6
+; CHECK-NEXT: return $0
+ %v = tail call i32 @quux2(ptr byval(i32) %x, ptr byval(i32) @global)
+ ret i32 %v
+}
+
+define i32 @mismatched_byval_duplicated(ptr byval(i32) %x) {
+; CHECK-LABEL: mismatched_byval_duplicated:
+; CHECK: .functype mismatched_byval_duplicated (i32) -> (i32)
+; CHECK-NEXT: # %bb.0:
+; CHECK-NEXT: global.get $push2=, __stack_pointer
+; CHECK-NEXT: i32.const $push3=, 16
+; CHECK-NEXT: i32.sub $push11=, $pop2, $pop3
+; CHECK-NEXT: local.tee $push10=, $1=, $pop11
+; CHECK-NEXT: global.set __stack_pointer, $pop10
+; CHECK-NEXT: i32.load $push0=, 0($0)
+; CHECK-NEXT: i32.store 12($1), $pop0
+; CHECK-NEXT: i32.load $push1=, 0($0)
+; CHECK-NEXT: i32.store 8($1), $pop1
+; CHECK-NEXT: i32.const $push6=, 12
+; CHECK-NEXT: i32.add $push7=, $1, $pop6
+; CHECK-NEXT: i32.const $push8=, 8
+; CHECK-NEXT: i32.add $push9=, $1, $pop8
+; CHECK-NEXT: call $0=, quux2, $pop7, $pop9
+; CHECK-NEXT: i32.const $push4=, 16
+; CHECK-NEXT: i32.add $push5=, $1, $pop4
+; CHECK-NEXT: global.set __stack_pointer, $pop5
+; CHECK-NEXT: return $0
+ %v = tail call i32 @quux2(ptr byval(i32) %x, ptr byval(i32) %x)
+ ret i32 %v
+}
+
+; TODO: We could optimize this to forward the byval argument without copying and
+; tail call.
+define i32 @matched_byval(ptr byval(i32) %x) {
+; CHECK-LABEL: matched_byval:
+; CHECK: .functype matched_byval (i32) -> (i32)
+; CHECK-NEXT: # %bb.0:
+; CHECK-NEXT: global.get $push1=, __stack_pointer
+; CHECK-NEXT: i32.const $push2=, 16
+; CHECK-NEXT: i32.sub $push8=, $pop1, $pop2
+; CHECK-NEXT: local.tee $push7=, $1=, $pop8
+; CHECK-NEXT: global.set __stack_pointer, $pop7
+; CHECK-NEXT: i32.load $push0=, 0($0)
+; CHECK-NEXT: i32.store 12($1), $pop0
+; CHECK-NEXT: i32.const $push5=, 12
+; CHECK-NEXT: i32.add $push6=, $1, $pop5
+; CHECK-NEXT: call $0=, quux, $pop6
+; CHECK-NEXT: i32.const $push3=, 16
+; CHECK-NEXT: i32.add $push4=, $1, $pop3
+; CHECK-NEXT: global.set __stack_pointer, $pop4
+; CHECK-NEXT: return $0
+ %v = tail call i32 @quux(ptr byval(i32) %x)
+ ret i32 %v
+}
+
declare i32 @var(...)
define i32 @varargs(i32 %x) {
; CHECK-LABEL: varargs:
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